This invention is directed to a general-purpose radiographic film that can be rapidly processed and directly viewed. In addition, the radiographic film of this invention also has what is known as xe2x80x9cvisually adaptive contrastxe2x80x9d because it can provide higher contrast than normal in the higher density regions of an image. This invention also provides a film screen imaging assembly for radiographic purposes, and a method of processing the film to obtain a black-and-white image.
Over one hundred years ago, W. C. Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913, Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation (X-rays). Today, radiographic silver halide films account for the overwhelming majority of medical diagnostic images. Such films provide viewable black-and-white images upon imagewise exposure followed by processing with the suitable wet developing and fixing photochemicals.
In medical radiography an image of a patient""s anatomy is produced by exposing the patient to X-rays and recording the pattern of penetrating X-radiation using a radiographic film containing at least one radiation-sensitive silver halide emulsion layer coated on a transparent support. X-radiation can be directly recorded by the emulsion layer where only low levels of exposure are required. Because of the potential harm of exposure to the patient, an efficient approach to reducing patient exposure is to employ one or more phosphor-containing intensifying screens in combination with the radiographic film (usually both in the front and back of the film). An intensifying screen absorbs X-rays and emits longer wavelength electromagnetic radiation that the silver halide emulsions more readily absorb.
Another technique for reducing patient exposure is to coat two silver halide emulsion layers on opposite sides of the film support to form a xe2x80x9cdual coatedxe2x80x9d radiographic film so the film can provide suitable images with less exposure. Of course, a number of commercial products provide assemblies of both dual coated films in combination with two intensifying screens to allow the lowest possible patient exposure to X-rays. Typical arrangements of film and screens are described in considerable detail for example in U.S. Pat. No. 4,803,150 (Dickerson et al), U.S. Pat. No. 5,021,327 (Bunch et al) and U.S. Pat. No. 5,576,156 (Dickerson).
Radiographic films that can be rapidly wet processed (that is, processed in an automatic processor within 90 seconds and preferably less than 45 seconds) are also described in the noted U.S. Pat. No. 5,576,156. Typical processing cycles include contacting with a black-and-white developing composition, desilvering with a fixing composition, and rinsing and drying. Films processed in this fashion are then ready for image viewing. In recent years, there has been an emphasis in the industry for more rapidly processing such films to increase equipment productivity and to enable medical professionals to make faster and better medical decisions.
As could be expected, image quality and workflow productivity (that is processing time) are of paramount importance in choosing a radiographic imaging system [radiographic film and intensifying screen(s)]. One problem with known systems is that these requirements are not necessarily mutually inclusive. Some film/screen combinations provide excellent image quality but cannot be rapidly processed. Other combinations can be rapidly processed but image quality may be diminished. Both features are not readily provided at the same time.
In addition, the characteristic graphical plots [density vs. log E (exposure)] that demonstrate a film""s response to a patient""s attenuation of X-ray absorption indicate that known films do not generally provide desired sensitivity at the highest image densities where important pathology might be present. Traditionally, such characteristic sensitometric xe2x80x9ccurvesxe2x80x9d are S-shaped. That is the lower to midscale curve shape is similar to but inverted in comparison with the midscale to upper scale curve shape. Thus, these curves tend to be symmetrical about a density midpoint.
Another concern in the industry is the need to have radiographic films that as accurately as possible show all gradations of density differences against all backgrounds. It is well known that the typical response of the human eye to determining equal differences in density against a background of increasing density is not linear. In other words, typically it is more different for the human eye to see an object against a dark background than it is to see an object against a lighter background. Therefore, when an object is imaged (for example using X-rays, with or without intensifying screens) at the higher densities of the sensitometric curves, it is less readily apparent to the human eye when the radiographic film is being viewed. Obviously, this is not a desirable situation when medical images are being viewed and used for important diagnostic purposes.
In order to compensate for this nonlinearity of response by the human eye, it would be desirable to somehow increase radiographic film contrast only at the higher densities without changing contrast or other properties at lower densities. The result of such a modification would be a unique sensitometric curve shape where the contrast is higher than normal in the higher density regions. Such a curve shape is considered as providing xe2x80x9cvisually adaptive contrastxe2x80x9d (VAC).
While this type of sensitometry sounds like a simple solution to a well known problem, achieving it in complicated radiographic film/screen systems is not simple and is not readily apparent from what is already known in the art. Moreover, one cannot predict that even if VAC is obtained with a particular radiographic film, other necessary image properties and rapid processability may be adversely affected.
Exposure and processing conditions for radiographic films vary widely throughout the world. Processing equipment ranges from very expensive sophisticated automatic film processors to simple shallow tray, low cost processors for manual processing. Exposure can be carried out with modern triple-phase X-ray generators or older single-phase generators. These older generators usually have low power and are quite variable in their output of X-radiation.
Because of the wide variability of the conditions for using radiographic films, there is a need in the industry for a radiographic film that is readily exposed and processed to provide a sensitometric curve shape that is suited to record variables exposures. Such a film could be used throughout the world under a wide variety of conditions without sacrificing quality of image and processability.
The present invention provides a solution to the noted problems with a radiographic silver halide film comprising a support having first and second major surfaces and that is capable of transmitting X-radiation,
the film having disposed on the first major support surface, one or more hydrophilic colloid layers including a single silver halide emulsion layer, and on the second major support surface, one or more hydrophilic colloid layers including a single silver halide emulsion layer,
each of the silver halide emulsion layers comprising silver halide grains that (a) have the same or different composition in each silver halide emulsion layer, (b) account for at least 50% of the total grain projected area within each silver halide emulsion layer, (c) have an average thickness of less than 0.3 xcexcm, and (d) have an average aspect ratio of greater than 5,
all hydrophilic layers of the film being fully forehardened and wet processing solution permeable for image formation within 45 seconds,
the film being free of particulate dyes, and
the film being capable of providing an image with visually adaptive contrast whereby the upper scale contrast is at least 1.5 times the lower scale contrast of a sensitometric D vs. log E curve.
This invention also provides a radiographic imaging assembly comprising the radiographic film described above provided in combination with an intensifying screen on either side of the film.
Further, this invention provides a method comprising contacting the radiographic film described above, sequentially, with a black-and-white developing composition and a fixing composition, the method being carried out within 90 seconds to provide a black-and-white image with visually adaptive contrast whereby the upper scale contrast is at least 1.5 times the lower scale contrast of a sensitometric D vs. log E curve.
The present invention provides a radiographic film and film/intensifying screen assembly that gives the medical professional a greater ability to see an object against a dark (or high density) background. Therefore, when an object is imaged using the film of this invention at the higher densities, the object is more readily apparent to the human eye.
In order to compensate for the nonlinearity of response by the human eye, the radiographic film contrast has been increased only at the higher densities without changing contrast or other properties at lower densities. The result of such a modification is a unique sensitometric curve shape where the contrast is higher than normal in the higher density regions. Thus, the films of this invention are considered as providing xe2x80x9cvisually adaptive contrastxe2x80x9d (VAC) as we defined it.
Moreover, the film of this invention has specifically designed emulsion layers to provide flexibility for use with a wide variety of exposure and processing conditions needed for a general purpose film throughout the world.
In addition, all other desirable sensitometric properties are maintained and the films can be rapidly processed in conventional processing equipment and compositions.